Rolling steel in ferritic state



Feb.

Filed May 12, 1960 TENS/LE STRENGTH (P67) S. EPSTEIN ETAL ROLLING STEELIN FERRITIC STATE I Hon/'64 mm,

5 Sheets-Sheet l i i i .049 .0/0 ./4

EL o/ven r/o/v mvo R5006 7/0/1/ (Z) 0 A200 /400 I500 Hoe-Fo/wnr/o/vTEMPE/MTURE KAI/v65 TE 5 7711/6 TEMPERA TUBE "F I INVENTORS Samuel'psfem c/qbn W. Frame and George E Mel/0y BY ATTORNEY Feb. 5, 1963 FiledMay 12, 1960 TENS/LE STRE/VG 71/ (P51) 5. EPSTEIN ETAL 3,076,361

ROLLING STEEL IN FERRITIC STATE 3 Sheets-Sheet 3 HIGH TE MPE RA TURETENS/LE TEST 66 may SPEED 0/0405 I l x I I 2a000 i-DEFORMHT/0/VINVENTORS Samuel Epsl'e/n John M Frame aha/ eorge F. Mel/0 ATTORNEYUnited States Patent Ofifice 3,076,361 Patented Feb. 5, 1963 3,076,361ROLLENG STEEL IN FERRITIC STATE Samuel Epstein, John W. Frame, andGeorge F. Melloy, Bethlehem, Pat, assignors to Bethlehem Steel Company,a corporation of Pennsylvania Filed May 12, 1960, Ser. No. 28,808 19Claims. (Cl. 80-60) subject to appreciable decarburization and scalingwhich are very serious surface defects. These greatly detract from thequality of the finished product, especially where high surface hardnessis necessary as' in tool steel. nitriding steel, for example,decarburization causes the nitrided layer to be weak and brittle.Decarburization that at which any substantial work hardening takes placeduring rolling.

Bars rolled by conventional hot rolling methods must frequently be slowcooled or subjected to various thermal treatments to avoid defects suchas cooling cracks, thermal ruptures, etc., associated with rapid coolingfrom the rolling temperature. Such treatments are unnecessary with barsproduced by our method as above described.

We find that bars produced from billets in accordance with our processhave excellent surface finish. The bars are substantially free fromdecarburization and scale and therefore do not require correctivesurface treatment. Bars rolled by our method retain the metallurgicaland mechanical properties of the billets from which they are formed.

FIGS. 1, 2 and 3 are graphs of high temperature tensile tests, showingtensile strength, elongation, and reduction of area at varioustemperatures of a 10-120 grade tool steel, of a nitriding steel, and ofa high speed steel, re-

' spectively. In these graphs it is evident that the tensile and scalingmay add materially to the cost of grinding" the steel and otherwisepreparing the surface of the product for its use in service.

Decarburization is highly undesirable and it therefore is necessary toremove the decarburized'surface by grinding, or to restore carbon by arecarburization treatmentboth processes being expensive and undesirable.

Furthermore, after normal high temperature rolling such steels usuallymust be cooled slowly from the rolling temperature to avoid excessivehardening, high residual stresses, cooling cracks, etc., and thereaftermust normally be annealed or otherwise .heat treated in order to attainthe desired metallurgical and mechani al P P- erties. Such heattreatment also causes decarburization and scaling.

Furthermore, with normal high temperature rolling is difiicult to attainan excellent surface finish.

It is therefore a broad object of this invention to provide a processfor rolling steels which avoids the dangers of decarburization andscaling, etc. as mentioned above, and produces a rolled product ofexcellent surface finish and desired metallurgical and mechanicalproperties.

In the practice of our process we subject a billet of steel produced byconventional means to the following treatment:

(1) The billet is first given the heat treatment necessary to producethe properties desired in the finished bar.

In normal prior hot rolling practice this heat treatment would be givento the bars after rolling, because the eifects of any treatment given tothe billet would be lost in the hot rolling. Such heat treatments mayconsist of annealing, normalizing, spherodize annealing, quenching andtempering, or other treatment processing designed to produce a producthaving specified physical properties.

(2) The billet is then treated by conventional methods to remove scaleand decarburization. Such methods include chipping, scarfing, turning,grinding and/ or pickling.

(3) The billet is then heated to a temperature not higher than the lowercritical temperature, on heating, of

the'steel (the A temperature) and not lower than 200 F. below the Atemperature, and rolled to finished size while maintaining thetemperature of the steel within said 'at' which'it 'is 'still' ferritic.40"

In fact, the tensile strength and the plasticity of the steel at theupper temperatures at which the steel is still ferritic approximate thatof steel heated to the normal the upper critical temperature of thesteelr hot-rolling temperatures several hundred degrees above The graphsof FIGS. 1, 2 and 3 also indicate that upon heating to a temperaturesomewhat above the lower critical temperature on heating (thetemperature A in the graphs) the tensile strength rises' and theductility falls.

' This is because the austenitic condition of the steel in thesetemperature ranges has somewhat higher strength and lower ductility thanthe steel hasin the upper temperatures heatthe steel above the Acritical temperature.

range. We prefer to roll at a temperature as close to the A temperatureas possible, preferably not more than 50 to 100 F. below the Atemperature. The temperature range will vary for different steels andshould be above The temperature range below the A temperature, withinwhich we roll will vary with different steels. The 2 data in the graphsofFIGS. 1, 2 and 3 indicate that the tool steel illustrated, containingcarbon 1.18%, manganese .41%, phosphorus 019%, sulphur 018%, silicon.14%, has properties making it suitable for hot-rolling within anapproximate temperature range of about 1380 F. to 1270 F.; thatthe-nitriding steel illustrated, containing carbon .42%, mangauese .63%,phosphorus .026%, sul- 'phur 026%, silicon 32%,chromium'1.57,%,-molybdenum 34%, and aluminum 1.10% has properties mak--ing it suitable for hot-rolling within an approximate temperature rangeof about 1470 F. to 1350 'F.; that the high speed steel illustrated,containing carbon .83%, chromium 3.97%, molybdenum 4.73%,tungsten'6.37%,- and vanadium 1.88% has properties making it suitable-for hotrolling within an approximate temperature range of about 1520 F. tol350F. These temperature ranges l have been indicated by the verticaldot-dash broken lines in the graphs. In some cases it may be necessarytorestrict the range of rolling temperatures still further in order toavoid exceeding the annealed hardness. For instance, if his desired toretain the original annealed hardness of high speed steels such as shownin FIG; 3 a rolling range going no lower than F. below the A temperatureis necessary.

Generally speaking, the rolling temperature should beas close to the Atemperature as possible, and above the temperature at which the tensilestrength begins to rise" steeply and the ductility begins to fallrapidly with small" p Accordingly it is essential whenrolling inaccordance with our invention not to,

decreases in temperature, as shown in the drawings. Rolling attemperatures below this lower limit may result in breaks, corner andsurface tears, and excessive hardening. Although the temperature rangesappear to be narrow, in practice the heat gained in deforming the steelin the various roll passes offsets to a large extent the normal heatlosses, making it quite feasible to keep the steel in the desiredtemperature range. No reheating is necessary. We have'found that thelower limit for successful rolling lies approximately 200 F. below thelower critical temperature; on heating, of the steel being rolled.However, it is preferable to maintain the steel at a temperature notmore than 50 to 100 below the A temperature. It should be pointed outthat each type of steel and even specific analyses of steel within suchtypes, have ideal lower limits of temperature above which rolling willbe most successful.

Among the various steels which have been investigated and which exhibita similar temperature range for hot rolling in the ferritic state arethose steels which fall within the following ranges of composition:

0, Mn, P, 8, r percent percent percent percent percent It was desired toproduce bars having a maximum Brinell hardness of 187. These billetswere normalized Carbon Tool Steel 0, percent Mn, percent Si, percent Cr,percent; Al,percent Mo, percent V, percent W, percent l.lll.fi0 I l.,45.10 20 A BallBearlng Steel Alb/1.10 I .25/.45 .20l.35 1.20/l.50 INltrlding Steel .08I.45 .40[.70 .20I.40 1.40/L80 .8 5/L2 0 .30I.45

High Speed Steels 1131158 3131'. :38 33;: 213.5% 7 2585313 "Tilt?11121137 Automotive Axle Steel 7 32/19 170 .00 l5/.'30 I i 7 FreeMachlning Steel .12: max. 4011.00 .o1-.12 .1e-.2a

It is here pointed out, however, that these steels are only a fewexamples of non-austenitic steels which can be advantageously rolled bythe process of our invention. Theinvention is applicable to all steelswhich are normally non-austenitic.

For example, a nitriding steel having a lower critical temperature, onheating, of 1440 F. was rolled between 1.420 F. starting temperature and1400" F. finishing temperature without substantial work hardening; and aC1018 carbon steel having a lower critical temperature of- 1370 F. wasrolled in a temperature range of 1370 F. to 1350* F. without substantialwork hardening.

To'give a typical example of our procedure the follow ing nitridingsteel was rolled according to the invention.

0, Mn, P, 8, Si, Cr, Mo, Al, percent percent percent percent percentpercent percent percent .38 .00 i .015 l .001 .28 l 1.50 .37 1.17

at 1600 F. and spheroidized at a temperature of 1420" F. to a hardnessof Brinell, and the surface defects removed by grinding. The billetswere then heated to 1300 F. and rolled into bars at this temperature,which is approximately 55 F. below the lower critical temperature, onheating, for this steel. The final hardness of the rQlled bars was163-170 Brinell.

We have found that sections difficult to roll, such as sharp corneredsquares, can be rolled by our process.

In ordinary hot rolling, breaks and tears are more apt to form in highercarbon and highly alloyed steels, and this may also occasionally be truein our low temperature warm rolling process. But just as breaks andtears can be avoided during ordinary hot rolling of these more sensitivehigher carbon highly alloyed steels by paying special attention toproper grinding and annealing of the billets before rolling and bynormal adjustments of the roll passes, so also, breaks and tears in themore sensitive steels can be avoided in the same way in our warm rollingprocess.

When conditioning billets prior to warm rolling by scarfing andpickling, light scabs may show on the bars after rolling, but when theconditioning is done by chipping instead of scarfing, and then pickling,no such scabs appear and a very good surface is obtained-much betterthan the surface obtained by ordinary hot rolling at temperatures highabove the upper critical.

As has been stated, the surface of the warm rolled steel is especiallygood. The surface is of good enough quality to permit the use of suchwarm rolled product in automatic cutting machines without cleaning thewarm rolled steel, cold drawing it, machining it, or the like,preparatory to feeding it into the automatic cutting machine.

It will be clearly apparent from the foregoing description that ournovel low temperature process as defined in the claims will have manyadvantages over the prior art rolling processes which take place at muchhigher temperatures in the austenitic state, e.g., we have discoveredthe following advantages:

, (1) Substantially no decarburization occurs on the rolled bars.Accordingly, subsequent treatment of the bars to remove decarburizationor to restore carbon is unnecessary.

- (2) Formation of scale is substantially avoided thereby eliminatingthe need for removing the scale.

(3) Superior surface finish.

(4) Better sizing.

(5) Slow cooling after rolling into bars is not required.

(6) The rolled bars retain the metallurgical and mechanical propertiesof the billets from which they are formed;

While we have thus described our invention in considerable detail we donot wish to be limited narrowly to the exact and specific particularsdisclosed, but we may also use such substitutes, modifications, orequivalents as are included within the scope and spirit of the inventionor pointed out in the appended claims.

We claim: 1 r

T 1..The method of producing rolled shapes of non-austenitic steelcomprising normalizing a billet, spheriodizing said billet, removingscale and decarburization from said billet, heating the said billet to atemperature within a range not higher than the lower criticaltemperature, on heating, of said steel and not lower than 100 F. belowsaid critical temperature, and rolling said steel while within saidtemperature range.

2. The 'metho'd fproducing rolled shapes of nonaustenitic steelcomprising normalizing a billet, spheroidizing said billet", -removingscale and decarburization from said billet, heating the said billet to atemperature within a range not higher than the lower criticaltemperature, on heating, of said'steeland'not lower than 200 F. belowsaid critical temperature, and rolling said steel while within saidtemperature range.

3, The method of producing rolled shapes of nonaustenitic steelcomprising spheroidizing a billet, removing scale and decarburizationfrom said billet, heating the said billet to a temperature within arange not higher than the lower critical temperature, on heating, ofsaid steel and not lower than 100 F. below said critical temperature,and rolling said steel while within said temperature range.

4. The method of producing a rolled shape of nonaustenitic steelcomprising heat treating a billet to produce therein the metallurgicaland mechanical properties desired in the rolled shape, removing scaleand decarburizetion from said billet, heating the said billet to atemperature within a range not higher than the lower criticaltemperature, on heating, of said steel and not lower than 100 F. belowsaid critical temperature, and rolling said steel while within saidtemperature range.

5. A process for the rolling of a steel billet containing C .38-45%, Mn.40-.7-0%, Si ill-.40%, Cr 1.401.80 Al .85-1.20%, Mo .30.45%, balanceessentially iron, comprising heat treating a billet of said steel tobelow a desired maximum hardness, heating said steel billet to within atemperature range having as the upper limit thereof, the highesttemperature at which said steel billet will remain ferritic and havingas the lower limit thereof, a temperature of approximately 200 F. belowthe lower mean critical temperature, on heating, of said steel billet,and rolling said steel billet while within said temperature range andwhile maintaining said hardness below said desired maximum hardness.

6. A process for the rolling of a steel billet containing C .95l.l0%, Mn25-45%, Si .2-035%, Cr l.20l.50%, balance essentially iron, comprisingheat treating a billet of said steel to below a desired maximumhardness, heating said steel billet to within a temperature range havingas the upper limit thereof, the highest temperature at which said steelbillet is still ferritic and having as the lower limit thereof, atemperature of approximately 200 F. below the lower criticaltemperature, on heating, of said steel billet, and rolling said steelbillet while within said temperature range, and while maintaining saidhardness below said desired maximum hardness.

7. A process for the rolling of a steel billet containing C 19-86%, 'Mn35% max., Si .40% max., Cr 3.90- 4.40%, Mo 4.755.25%, V 1.752.05%, W604.75%, balance essentially iron, comprising heat treating a billet ofsaid steel to produce therein the metallurgical and mechanicalproperties desired in the rolled shape, heating said steel billet towithin a temperature range having as the upper limit thereof, thehighest temperature at which said steel billet will remain ferritic andhaving as the lower limit thereof, a temperature of approximately F.below the lower critical temperature, on heating, of said steel billet,and rolling said steel billetwhile within said temperature range, andwhile maintaining said properties.

8. A process for the rolling of a steel billet containing C .73-.83%, Mn.40% max., Si .40% max., Cr 3.604.10%, Mo 8.00-9.00%, V .90-1.20%, W1.40-

l.80%, balance essentially iron, comprising heat treating a billet ofsaid steel to produce therein the metallurgical and mechanicalproperties desired in the rolled shape, heating said steel billet towithin a temperature range having as the upper limit thereof, thehighest temperature at which said steel billet will remain ferritic andhaving as the lower limit thereof, a temperature of approximately 100 F.below the critical temperature, on heating, of said steel billet, androlling said steel billet while within said temperature range, and whilemaintaining said properties.

9-. A process for the rolling of a steel billet containing C 1.15 1.50%,Mn .20-.45%, Si .10-.20%, balance essentially iron, comprising heattreating a billet of said steel to produce therein the metallurgical andmechanical properties desired in the rolled shape, heating said steelbiilet to within a temperature range having as the upper limit thereof,the highest temperature at which said steel billet will remain whollyferritic and having as the lower limit thereof, a temperature ofapproximately 200 F. below the critical temperature, on heating, of thesaid steel billet, and rolling said steel billet While within saidtemperature range and while maintaining said properties.

10. Method of producing rolled shapes of non-austenitic steel havingclose dimensional tolerances, free from decarburization and scale, andof specified maximum hardness, comprising heat treating a billet of saidsteel to a hardness not greater than said specified maximum hardness,removing any decarburized and scaled areas from the surface of thebillet, heating the billet to a temperature within a range not higherthan the lower critical temperature, on heating, of said steel and notlower than approximately 200 F. below said critical temperature, androlling the billet to finished form while maintaining the temperature ofthe steel within said range.

11. A process for the hot-rolling of a non-austenitic steel billet whilein the ferritic state, comprising removing decarburization and scalefrom said steel billet, heating said steel billet to the upper range oftemperatures at which the steel is still ferritic, said range having asa lower limit thereof, a temperature of approximately 100 F. below thecritical temperature, on heating, of

said steel billet, and rolling said steel billet within said range.

12. A process for the hot rolling of a non-austenitic steel billet whilein the ferritic state, comprising removing decarburization and scalefrom said steel billet, heating said steel billet to the upper range oftemperatures at which the steel is still ferritic, said range having asa lower limit thereof a temperature of approximately 200 F. below thelower critical temperature, on heating, of said steel billet, androlling said steel billet while within said temperature range.

13. A process for the rolling of a steel billet containing C .38-.45%,Mn .40-.70%, Si .20.40%, Cr 1.40- 1.80%, Al .851.20%, Mo .30.45%,balance essentially iron, comprising removing decarburization and scalefrom said steel billet, heating said steel billet to within atemperature range having as the upper limit thereof, the highesttemperature at which said steel billet will remain ferritic and havingas the lower limit thereof, a temperature of approximately 200 F. belowthe lower critical temperature, on heating, of said steel billet, androlling said steel billet while within said temperature range.

14. A process for the rolling of a steel billet containing C .95-1.10%,Mn .25-.45%, Si .20-.35%, Cr 1.20- 1.50%, balance essentially iron,comprising removing decarburization and scale from said billet, heatingsaid steel billet to within a temperature range having as the upperlimit thereof, the highest temperature at which said steel billet isstill ferritic and having as the lower limit thereof, a temperature ofapproximately 200 F. below the lower critical temperature, onheating, ofsaid steel billet, and rolling said steel billet while within saidtemperature range.

15. A process for the rolling of a steel billet containing C .79-.86%,Mn 35% max., Si .40% max., Cr 3.90-4.40%, Mo 4.75-5.25%, V 1.75-2.05%, W6.0- 6.75%, balance essentially iron, comprising removingdecarburization and scale from said billet, heating said steel billet towithin a temperature range having as the upper limit thereof, thehighest temperature at which said steel billet will remain ferritic andhaving as the lower limit thereof, a temperature of approximately 100 F.below the lower critical temperature, on heating, of said steel billet,and rolling said steel billet while within said temperature range.

16. A process for the rolling of a steel billet containing C .73-.83%,Mn .40% max., Si .40% max., Cr 3.60- 4.10%, Mo 8.009.00%, V .90-1.20%, W1.40-1.80%, balance essentially iron, comprising removing decarburi-Zation and scale fromsaid billet, heating said steel billet to within atemperature range having as the upper limit thereof, the highesttemperature at which said steel billet will remain ferritic and havingas the lower limit thereofi, a temperature of approximately F. below thecritical temperature, on heating, of said steel billet, and rolling saidsteel billet while within said temperature range.

17. A process for the rolling of a steel billet containing C 1.15-l.50%,Mn .20.45%, Si .10.20%, balance essentially iron, comprising removingdecarburization and scale from said billet, heating said steel billet towithin a temperature range having as the upper limit thereof, thehighest temperature at which said steel billet will remain whollyferritic and having as the lower limit thereof, a temperature ofapproximately 200 F. below the critical temperature, on heating, of thesaid steel billet, and rolling said steel billet while within saidtemperature range.

18. The method of producing rolled shapes of nonaustenitic steelcomprising heat treating a billet of said steel to produce therein themetallurgical and mechanical properties desired in the rolled shape,heating said steel billet to within a temperature range having as theupper limit thereof, the highest temperature at which said steel billetwill remain ferritic and having as the lower limit thereof, atemperature of approximately 100 F. below the critical temperature, onheating, of said steel billet, and rolling said steel billet whilewithin said temperature range, and while maintaining said properties.

19. The method of producing rolled shapes of nonaustenitic steelcomprising heat treating a billet of said steel to produce therein themetallurgical and mechanical properties desired in the rolled shape,heating said steel billet to within a temperature range having as theupper limit thereof, the highest temperature at which said steel billetwill remain wholly ferritic and having as the lower limit thereof, atemperature of approximately 200 F. below the critical temperature,on'heating, of the said steel billet, and rolling said steel billetwhile within said temperature range and while maintaining saidproperties.

References Cited in the file of this patent The Making, Shaping andTreating of Steel, Seventh Edition, copyright 1957 by US. SteelCorporation.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No,3,076,361 February 5, 1963 Samuel Epstein et alt,

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below Columns 3 and .4, in the table, under the heading "HighSpeed Steels, and under the column heading "W, percent" for "L l/18.,"read lo l/108 column 5, line 68, for ".38--45%" read n38u45% column 6,line 6 for "25-45%" read .,2545% same line for ,2035%" read o 20 435%same column, line 18 for "e7986%" read .79.,86% 7 same line, for "35%max," read 035% max,

Signed and sealed this 3rd day of September 1963,

(SEAL) Attest' ERNEST W. SWIDER Attesting Officer DAVID L. LADDCommissioner of Patents

19. THE METHOD OF PRODUCING ROLLED SHAPES OF NONAUSTENITIC STEELCOMPRISING HEAT TREATING A BILLET OF SAID STEEL TO PRODUCE THEREIN THEMETALLURGICAL AND MECHANICAL PROPERTIES DESIRED IN THE ROLLED SHAPE,HEATING SAID STEEL BILLET TO WITHIN A TEMPERTURE RANGE HAVING AS THEUPPER LIMIT THEREOF, THE HIGHEST TEMPERATURE AT WHICH SAID STEEL BILLETWILL REMAIN WHOLLY FERRITIC AND HAVING AS THELOWER LIMIT THEREOF, ATEMPERATURE OF APPROXIMATELY 200*F. BELOW THE CRITICAL TEMPERATURE, ONHEATING, OF THE SAID STEEL BILLET, AND ROLLING SAID STEEL BILLET WHILEWITHIN SAID TEMPERATURE RANGE AND WHILE MAINTAINING SAID PROPERTIES.